Method for the preparation of stable aqueous dispersions of polymer beads and the use of these dispersions in photographic elements

Claim 1

Photographic element comprising a support and at least one silver halide emulsion layer wherein said element comprises in a layer of said photographic element and/or in the support thereof finely divided solid spherical polymer beads obtained by the steps of: (A) dissolving in an aqueous solvent mixture of water and at least one water-miscible polar organic solvent: (1) at least one α,β-ethylenically unsaturated monomer capable of forming a polymer that is soluble in the monomer(s) present in said aqueous solvent mixture but which is insoluble in said aqueous solvent mixture, (2) a free radical-forming polymerization initiator that is soluble in the aqueous solvent mixture, and (3) a graft-polymerizable polymer containing hydrophilic groups, and capable of forming a graft polymer that remains soluble in said aqueous solvent mixture, the weight ratio of said graft-polymerizable polymer to said monomer(s) being in the range from 1.5:100 to 8:100 and a weight ratio of polymerization initiator to monomer(s) from 0.1:100 to 5:100, and (B) heating the solution obtained to a temperature from 50° C. to the reflux temperature thereof with continuous stirring to initiate by polymerization the simultaneous massive formation of homopolymer or copolymer from said monomer and precipitation thereof, and the formation of a small porportion of graft polymer, said beads characterized in that they comprise a nucleus and an envelope which have different compositions, said nucleus being made up primarily of polymerized α,β-ethylenically unsaturated monomer(s) and said envelop being made up primarily of grafted polymer chains formed from said polymer containing hydrophilic groups and said α,β-ethylenically unsaturated monomer(s).